OLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
High-resolution organic light emitting display devices require transistors with high operation speeds, and existing technologies face challenges in effectively compensating for the threshold voltage of driving transistors, which affects the performance and efficiency of these devices.
Innovation Solution
The use of n-channel type transistors with a diode-connection method to internally compensate for the threshold voltage of the driving transistor, allowing for efficient current supply to the organic light emitting diode through a specific configuration of transistors and a storage capacitor, ensuring consistent operation across different voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If n-channel type transistors are used to achieve high operation speeds, then the operation speed is improved, but the threshold voltage variations affect the performance and efficiency
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the emission period through a dedicated compensation period. The driving transistor is configured in diode connection mode during this period, allowing the storage capacitor to be pre-charged to a voltage that compensates for the threshold voltage. This preliminary compensation ensures that threshold voltage variations do not affect the subsequent emission performance, thereby maintaining performance consistency while using high-speed n-channel transistors.
2Reliability
If diode-connection method is used to compensate threshold voltage, then threshold voltage compensation is achieved, but additional control periods and signal management are required
Solution Approach 1:
The patent applies universality by designing the driving transistor to serve multiple functions: it acts as a switching transistor during normal operation and as a diode-connected compensation element during the compensation period. The same transistor structure and components (storage capacitor, emission control signals) are used for both threshold voltage compensation and current control functions. This multi-functionality reduces the need for separate dedicated compensation circuits, thereby limiting the increase in device complexity while achieving reliable threshold voltage compensation.
3Manufacturing precision
If multiple transistors and storage capacitor are configured for current supply, then current control precision is improved, but the device structure becomes more complex
Solution Approach 1:
The patent applies merging by integrating the compensation function into the existing current control circuitry. The driving transistor, storage capacitor, and emission control signals are used jointly for both threshold voltage compensation and emission current control. The first and second emission control signals work together to control different transistors in sequence, merging the compensation operation and emission operation into a unified control scheme. This integration achieves precise current control while limiting the increase in device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables high-speed operation of n-channel type transistors, effectively compensating for threshold voltage variations, thereby enhancing the performance and efficiency of organic light emitting display devices by maintaining consistent current levels and brightness, independent of the driving transistor's threshold voltage.
Implementation Method 1
an organic light emitting diode including an anode electrode, and a cathode electrode configured to receive a second power source
Data Source
AI summary
A pixel includes a driving transistor including a gate connected to a first node, a first electrode connected to a second node, and a second electrode connected to an OLED, a first transistor configured to receive a first emission control signal and connected between a first power source and the second node, a second transistor configured to receive a scan signal and connected between the first and second nodes, a third transistor configured to receive the scan signal and including a first electrode configured to receive a data voltage, and a second electrode connected to a third node, a fourth transistor configured to receive a second emission control signal and connected between the third node and the OLED, a fifth transistor configured to receive the scan signal and connected between the OLED and an initializing power source, and a storage capacitor connected between the first node and the third node.